1. Field of the Invention
The present invention relates to a metal-bonded grinding tool obtained by fixing abrasive grains to a base of a tool by means of a metal bond matrix.
2. Description of the Related Art
A known method of manufacturing metal-bonded grinding tools involves mixing abrasive grains with a metal powder, compacting the mixture into a given shape, and sintering the green compact integrally with a base of a tool, thereby fixing the abrasive grains to the base of the tool (impregnated sintered tool). Another known method for manufacturing metal-bonded grinding tools involves placing abrasive grains on a base of a tool, and applying nickel plating (electrically or chemically) so as to cover the abrasive grains with nickel metal deposited, thereby mechanically fixing the abrasive grains to the base by means of the deposited nickel metal.
These conventional metal-bonded grinding tools, however, have a problem. Since the abrasive grains are fixed only mechanically to the metal bond matrix, the force of retaining the abrasive grains by means of the metal bond matrix is weak, thereby causing the abrasive grains to fall out of the metal bond matrix in a relatively short period of time. Another problem is that since the height of each abrasive grain projecting from the metal bond matrix is small, an exposed portion of the metal bond matrix comes into contact with a workpiece to be ground and thereby tends to cause contact resistance and erosion wear, resulting in the degraded grinding ability and durability of the grinding tool.
The erosion wear of the metal bond matrix easily caused in the conventional metal-bonded grinding tools as described above gives rise to a further problem. When the abrasive grains become exposed from the metal bond matrix by erosion wear of the metal bond matrix, such abrasive grains easily fall out of the metal bond matrix because no chemical bonding between the metal bond matrix and the abrasive grains. This significantly reduces the usability of the abrasive grains, thereby causing unstable grinding and significantly shortening the life of the tool.
A metal-bonded grinding tool capable of solving the above-described conventional problems has been proposed by the present applicant (see Japanese Patent Laid-open No. 2001-25969). The metal-bonded grinding tool described in this document is characterized in that abrasive grains are bonded to a base of the tool by means of a metal bond matrix containing a Cu alloy as a main component, wherein the metal bond matrix contains a material selected from a group consisting of Ti, Al, and a mixture thereof. Such a metal-bonded grinding tool is advantageous in that Ti, a Ti compound, Al, or an Al compound has a property capable of making abrasive grains wet by its reducing ability, to form chemical bonding between the metal bond matrix and the abrasive grains, thereby strongly bonding the abrasive grains to the metal bond matrix. This prevents the abrasive grains from falling out of the metal bond matrix, thereby keeping a stable grinding performance for a long time.
The metal-bonded grinding tool described in the above-described document has a high grinding performance capable of satisfying general grinding requirements, but as a result of examination of the present inventor, it was confirmed that such a metal-bonded grinding tool may often cause an inconvenience that the abrasive grains fall out of the metal bond matrix when used for grinding a very hard material such as stone for a long time.